EE 5 Electrical Machines 1 PDF

INTRODUCTION TO DC MACHINES Energy and Electromechanical Energy Conversion EE 5 – ELECTRICAL MACHINES 1 1 Preference for Electricity Energy is vital for all living-beings on earth. Modern lifestyle has further increased its importance, since a faster life means fast...

INTRODUCTION TO DC MACHINES Energy and Electromechanical Energy Conversion EE 5 – ELECTRICAL MACHINES 1 1 Preference for Electricity Energy is vital for all living-beings on earth. Modern lifestyle has further increased its importance, since a faster life means faster transport, faster communication, and faster manufacturing processes. All these lead to an increase in energy required for all those modern systems. “Energy can neither be created nor be destroyed”. We can only change its forms, using appropriate energy conversion processes. 2  Types Of Energy Sources Converted Into Electrical Energy Chemical Energy – energy that is released as the result of electron interactions Ex. Batteries (Dry Cell, Wet Cell and Fuel Cell) 3 Types Of Energy Sources Converted Into Electrical Energy Solar Energy – is light and heat energy from the sun This is the energy that is produced by the sunlight. The photovoltaic cells are exposed to sunlight based on the form of electricity that needs to be produced. The light from the Sun, made up of packets of energy called photons, falls onto a solar panel and creates an electric current through a process called the photovoltaic effect. Each panel produces a relatively small amount of energy but can be linked together with other panels to produce higher amounts of energy as a solar array. The electricity produced from a solar panel (or array) is in the form of direct current (DC). https://esdsolar.com/how-does-solar-energy-work/ 4  Types Of Energy Sources Converted Into Electrical Energy Solar Energy A solar power plant uses sunlight to get energy. As the sunlight is ample and renewable, one can use it to power up the home and business premises. If you install a solar power plant , you might need to spend upfront. However, it will minimize your energy consumption significantly. Mostly two key technologies have been used to use solar power to generate energy. These are photovoltaic solar technology and solar thermal technology. The photovoltaic technology will directly convert the sunlight into electricity, while the solar thermal technology will capture the heat of the sun. After capturing the heat, it will be converted into mechanical energy, and then it will turn into electricity. The photovoltaic technology will use panels of semiconductor cells to directly generate electricity. 5 Types Of Energy Sources Converted Into Electrical Energy Wind Energy – moving air turns the blades of large windmills or generator to make electricity. Wind energy is generated by harnessing the power of wind and mostly used in operating water pumps for irrigation purposes. It can be economically used for the generation of electrical energy. Winds are caused by two main factors: (i) Heating and cooling of the atmosphere which generates convection currents. Heating is caused by the absorption of solar energy on the earth’s surface and in the atmosphere. (ii) The rotation of the earth with respect to atmosphere and its motion around sun. https://www.istockphoto.com/illustrations/diagram-of-wind-energy 6  Types Of Energy Sources Converted Into Electrical Energy Hydroelectric Energy – fast flowing water released from dams in mountains areas can turn water turbines to produce electricity. Hydroelectric power stations, use the kinetic energy of moving water to drive turbines. A generating station which utilizes the potential energy of water at a high level for generation of electrical energy is known as a hydroelectric power station. In this case, water is allowed to flow from a higher level through a turbine where the potential energy of water is converted to kinetic energy and the turbine, in turn, rotates a generator to produce electricity. Hydroelectric generation is the fastest to respond to increasing power demands, reaching full power in two to three minutes. These plants can provide both base-load and peak- load demands for power at a relatively low cost, provided sufficient water is available. 7 Types Of Energy Sources Converted Into Electrical Energy Geothermal Energy – uses heat energy from the beneath the surface of the earth 1. Hot water is pumped from deep underground through a well under high pressure. 2. When the water reaches the surface, the pressure is dropped, which causes the water to turn into steam. 3. The steam spins a turbine, which is connected to a generator that produces electricity. 4. The steam cools off in a cooling tower and condenses back to water. 5. The cooled water is pumped back into the Earth to begin the process again. 8  Types Of Energy Sources Converted Into Electrical Energy Other Fuels for Heating Water turning into Steam: Coal Gas Petroleum Uranium Pagbilao Energy Corporation (PEC) is a joint venture between AboitizPower and TeaM Energy The coal-fired plant was inaugurated on May 31, 2018, and generates a baseload power of 420 MW. 9 Types Of Energy Sources Converted Into Electrical Energy Nuclear Energy – exists as stored energy which is released as a result of particle interactions with or within the nucleus Examples: Radioactive Decay – unstable nucleus, radio isotope decays to a more stable configuration Fission – heavy mass nucleus absorbs a neutrons and splits up into 2 or more nuclei with energy released Fusion – 2 light mass nuclei combine to produce more stable configuration with energy released. 10  Principle of Electromechanical Energy Conversion An electromechanical conversion device is a link between electrical and mechanical system. The purpose of electro-mechanical conversion device is to change the form of energy. When it is converting mechanical input to electrical output the device is generating. With electrical input, when mechanical output is obtained, the device is motoring. A device can work either as a generator or as a motor, provided pertinent conditions are satisfied for the concerned mode of operation 11 Dynamo A dynamo is a rotating electrical machine that converts mechanical energy into electrical energy or electrical energy into mechanical energy Two principles of dynamo are: Generator Action – it involves the development of voltage Motor Action – it involves the development of force or torque 12  Practical Generator DC generators are similar to dc motor in appearance and construction. They have the same stationary and rotating part which consist of the following essential parts Magnetic Frame or Yoke Pole-Cores and Pole-Shoes Pole Coils or Field Coils Armature Core Armature Windings or Conductors Commutator Brushes and Bearing 13 Practical Generator Frame or Yoke The outer frame or yoke serves double purpose: It provides mechanical support for the poles and acts as a protecting cover for the whole machine. It carries the magnetic flux produced by the poles 14  Practical Generator Pole Cores and Pole Shoes The field magnets consist of pole cores and pole shoes. The pole shoes serve two purposes: they spread out the flux in the air gap and also, being of larger cross-section, reduce the reluctance of the magnetic path they support the exciting coils (or field coils) 15 Practical Generator Pole Coils The field coils or pole coils consists of copper wire or strip, are wound coil placed over the core of the poles. The field windings are constructed into three types: a shunt field in which there are many turns of fine wire a series field with few turns of heavy wire a compound field in which both a shunt and series windings are used 16  Practical Generator Armature Core It houses the armature conductors or coils and causes them to rotate and hence cut the magnetic flux of the field magnets. Armature Windings virtually the heart of the dynamo, are insulated coils wound in the armature slots 17 Practical Generator Commutator The function of the commutator is to facilitate collection of current from the armature conductors. converts the alternating current induced in the armature conductors into unidirectional current in the external load circuit. Shaft - is made of steel and holds the commutator 18  Practical Generator Brushes and Bearings Brushes usually made of carbon, are held in a stationary position by brush holders. The brushes collect current from the commutator to the external circuit. The ball bearings are employed to freely rotate the commutator shaft and for quiter operation. 19 References  Bird, J. (2007). Electrical and Electronic Principles and Technology. (3rd ed.). Retrieved from https://www.pdfdrive.com  Sahdev, S. K. (2017). Electrical Machines  Rojas, R. A. 1001 Solve Problems in Electrical Engineering 20  ARMATURE WINDINGS & GENERATED EMF EE 5 – ELECTRICAL MACHINES 1 1 Types of Armature Windings The two general types of armature windings are: 1) Lap Winding 2) Wave Winding Elements or Conductors - the length of a wire lying in the magnetic field and in which an e.m.f. is induced, is called a conductor. Coil Span or Coil Pitch (Ys) - the coil span is the distance, measured in terms of Armature slots between the two sides of a coil. Ys = coil pitch, slots per pole S = total number of armature slots P = no. of poles k = any part of S/P that is subtracted from S/P to make Ys an integer 2  Lap Winding Lap winding forms a progressive loop as it expands around the periphery of the armature core. 3 Wave Winding Wave Winding forms a “wave” loop as it expands around the periphery of the armature core. 4  Uses of Lap and Wave Windings Lap and wave armature windings give the following characteristics and applications: 1) Wave winding gives more emf than lap winding 2) Wave winding is suitable for small generators at 500V – 600V circuits 3) Wave winding is used for high voltage low current machines 4) High current is used for lap winding because it gives more parallel paths 5) Lap winding is suitable for low voltage high current generators 5 General Voltage Equation Of A Generator Lap Winding Wave Winding 6  Sample Problems 7 Sample Problem 1 Calculate the coil pitches and indicate the slots into which the 1st coil should be placed for the following windings. a.) 57 slots, 4 poles b.) 132 slots, 8 poles Solution: a.) Ys = S/P – k b.) Ys = S/P – k = 57/4 = 132/8 = 14.25 = 16.5 = 14 = 16 = 1st & 15th slot = 1st & 17th slot 8  Sample Problem 2 Determine the commutator pitches Yc for the following armature windings. a.) 4 pole simplex lap b.) 229 segments 6 pole simplex wave Solution: b.) wave a.) lap c = 229 Yc =m P =6 m =1 m =1 Yc =1 Yc = (c +-m) / (P/2) = (229 +- 1) / (6/2) Yc = 76 &/or 77 9 Sample Problem 3 The armature of a 4-pole generator carries a total current of 300 amp. What current flows in each path if the winding is simplex wave? Solution: Ia’ = IT / a’ a’ = 2m =2x1 a’ =2 Ia’ = IT / a’ = 300/2 Ia’ = 150/path 10  Sample Problem 4 How many parallel paths are there in a 10-pole simplex lap winding? Solution: P = 10 m =1 a’ = mP = 1 x 10 a’ = 10 paths 11 Sample Problem 5 A four pole DC generator with lap winding has 48 slots and 4 elements per slot. How many coils does it have? Assume one conductor per coil side. Solution: P=4 1 coil -> 2 coil side Lap -> 2 conductors S = 48 Z/s = 4cond/slot No. of coils = ? No. of coils = 4 conductors/slot x 48 slots x 1coil/2conductors = 96 coils 12  Sample Problem 6 A four-pole generator having duplex wave wound armature winding has 51 slots, each slot contains 20 conductors. What will be the voltage generated in the machine when driven at 1500 rpm assuming the flux per pole to be 7 mwb? Solution: P=4 Z = 20cond/slot x 51 slot = 1020 cond wave S = 51 a’ = 2m =2x2 = 4 paths Z/S = 20cond/slot N = 1,500 rpm m=2 Eg = 1020 (4) (7x10^-3) (1500) φ = 7 mWb 60 x 4 Eg = ? Eg = 178.5 v 13 References  Bird, J. (2007). Electrical and Electronic Principles and Technology. (3rd ed.). Retrieved from https://www.pdfdrive.com  Sahdev, S. K. (2017). Electrical Machines  Rojas, R. A. 1001 Solve Problems in Electrical Engineering 14